The present invention relates to abrading apparatus of the type having an endless belt trained over a pair of spacedapart contact and idler rolls, and more particularly to an improved method and apparatus which includes provision for preventing the accumulation of abraded debris on the inside surfaces of the belt.
Conventional belt-type abrading apparatus include a power-driven contact roll and an idler roll mounted on a central support member which is connected to a frame structure. An endless, abrasive belt is trained over the rolls and an air space is defined between the central support member and inside surfaces of the belt. Operation of the contact roll will simultaneously impart motion to the belt. Typically, such abrading apparatus will also include a mechanism for oscillating the idler roll about an axis extending perpendicularly to the longitudinal axis of the idler roll. The oscillation causes a traveling belt to shift slightly back and forth so that belt imperfections do not result in streak marks or other flaws on abraded workpieces. The movement of the belt is commonly referred to as "steering".
A problem existing in the operation of abrading apparatus as described above results from the inflow of abraded debris from a workpiece into the air space located between inside surfaces of the belt. Apparently, abraded debris tends to be drawn into the air space due to movement of the belt which creates a lower pressure area adjacent the belt's edges. Additionally, in abrading apparatus used to abrade the lower surface of a workpiece (referred to as a "lower head"), it can be appreciated that abraded debris will migrate into the air space by virtue of gravity. The inflow of abraded debris to the air space results in a build up of the debris on the inside surfaces of the belt.
If the workpiece is lumber of a particularly resinous species, such as, for example, Ponderosa pine (Pinus ponderosa), the debris or fibers rapidly accummulate and adhere to the inside surfaces of the belt (as well as on the rolls) and prevent the belt from steering during oscillation of the idler roll. Steering is impeded because the rolls do not have a smooth surface and the belt will not shift readily therealong. Prevention of steering may result in the belt folding up on itself or creasing which may cause a split permanently damaging the belt.
In addition, the build up of abraded debris or fibers on the inside surfaces of the belt may result in shortened belt life because the inside surfaces are subjected to more wear and strain as they travel around the rolls. As a consequence, it is necessary to periodically remove abrasive belts and subject them to burdensome cleaning procedures. Of course, changing and cleaning of the belts and rolls is time consuming, and mill down time because of repairs to abrading apparatus is uneconomical.
Further, it should be noted that with accumulation of abraded debris or fibers as described above, an abrasive belt may have a relatively short life. For instance, it has been found that the maximum operating life for an abrasive belt in conditions resulting in debris accummulation on the belt is approximately 8 hours. It can readily be appreciated that prevention of accumulation of abraded debris on the inside surfaces would result in significantly longer belt life as well as preventing creasing and splitting of a belt during idler roll oscillation. Of course, longer belt life would also result in less down time required to change belts.
Accordingly, it is a general object of the present invention to improve conventional belt-type abrading apparatus so that the air space existing between the central support member and the inside surfaces of the belt is maintained at a pressure greater than the prevailing air pressure adjacent the outside surfaces of the belt. By maintaining the greater pressure in the air space, abraded debris will be prevented from inflowing to the air space and consequently accumulation of debris on the inside surfaces of the belt will be prevented. Accumulation on the rolls will also be eliminated. Unimpeded "steering" will be ensured and intervals required between belt cleaning will be significantly increased.
More particularly, it is an object of the present invention to provide a method and apparatus including a pressurizing means which utilizes an air mover means communicating with a duct means for delivering or inducing air into the air space on both sides of the central support member. It may be appreciated that the induced air will sweep over the inside surfaces of the belt and ensure that accumulation of abraded debris does not occur.
Another object of the present invention is to provide sealing means provided adjacent opposite ends of each roll and on opposite sides of the central support member for substantially sealing the air space. In effect, a plenum chamber will be created upon the introduction of air through the duct means, and this will prevent inflow of abraded debris. The sealing means will permit leakage of air outwardly from the air space, but will not permit inflow of abraded debris.
These and additional objects and advantages of the present invention will be more clearly understood from a consideration of the drawings and the detailed description of the preferred embodiment.